Max Edwards, Marketing Manager, Concep 

Being put on a blocklist can have severe implications for firms, yet it's a discussion that tends to be avoided between email service providers and marketers. Understanding how blocklists work is just the tip of the iceberg. It's our responsibility to educate you so you're best positioned to avoid the threat of blocklisting.

Best practices to avoid the threat of blocklisting

Creating & sending out email communication to key clients can mean hours of work for marketers. With all the effort that goes into managing a campaign, it’s important to ensure your emails have the best chance of reaching the intended inbox.

In this post, we’ll cover how you can steer clear of the threat of blocklisting by broadening your knowledge of data hygiene & deliverability, fine tuning your processes, and understanding the important role an ESP's infrastructure plays in driving the success of your eMarketing performance:

Data Hygiene

A large percentage of Professional Services deliverability issues stem from poor hygiene in marketing lists. The average rate of CRM data decay is about 30% a year (Marketing Insider Group), meaning that savvy marketers should be employing regular maintenance on their lists & databases. The key is to prevent any problematic email addresses from surfacing that may be flagged as spam or negatively impact your engagement metrics.

3 key ways to ensure that your firm is adhering to these best practices:

Regularly review the quality of your marketing lists – If you needed a compelling reason to keep your firm’s lists up to date, it’s blocklisting! Regularly sending to a high volume of old or unengaged contacts will not only register a significantly higher number of bounces, but affect the way that email clients like Outlook will folder your comms in the Spam or Other box. If you have a consistent amount of high bounce and spam rates, your poor sending reputation could get you blocklisted. Email service and internet providers monitor for spamming activity and may block your deliverability to an entire client due to 1 or 2 invalid emails on your list

Segment your lists – Segmenting your lists goes beyond separating contacts based on industry area or even preferences. You’ll likely find you have handfuls of contacts on each list with low to no engagement, which could be down to poor data, deliverability or a host of relationship-based reasons. Sending to inactive contacts is a waste of your email credits, there’s no point continuing to send to contacts who don’t show interest. Intuitively select who you send to, based on engagement score and deliver additional rich content to your most engaged contacts.

Think outside the box - Are you currently sending email campaigns to a high volume of contacts and seeing little to no engagement in key clients or prospects? Your contacts may not be interacting for several reasons; they simply might not be interested in your content, or your comms might not be hitting their inboxes. We advise you to first dive into reporting to assess the most likely culprit, then send more strategically to maximise your ability to hit the inboxes of those you're not reaching. In those cases, it's worth noting that email security filters are significantly more likely to mark HTML-based emails as spam compared to plain text. It would be beneficial to test the success of plain text campaigns with a handful of contacts that you're struggling to reach. You are far more likely to hit the inbox, and they will still have the option to open the HTML version in their browser if they're interested in the content. Win, win!


While cleaning your data is a great starting point, working with your ESP to configure email authentication is crucial to the success of your comms. Authentication helps to verify the digital identity of the sender and is commonly deployed through DKIM, DMARC and SPF.

The Sender Policy Framework (SPF) is a technique used to ensure that spammers can’t send emails on your behalf. You’ll probably find that this has already been set up within your firm by IT. This is a simple email validation system but combined with DKIM and DMARC, it becomes truly robust and offers protection against malicious attacks.

Domain Keys Identified Mail (DKIM) is another authentication method used to detect email spoofing –forged sender addresses. It allows the receiver of the email to validate that the email was both sent and authorized by the owner of the domain. DKIM pairs the email with a securely encrypted digital signature which is validated at a server level by the receiving system. It is known to improve deliverability.

Finally, Domain-based Message Authentication Reporting and Conformance (DMARC) uses SPF and DKIM to add the final string to the authentication bow. DMARC offers reporting that gives domain owners insights on emails being sent from their domain and if any have been sent on their behalf. These insights can help the owner gain control of any malicious email as well as support deliverability performance.

Enabling DKIM & DMARC is something that an ESP should provide as default. These are crucial authentication techniques, not add-ons! If you haven't had this setup, we would strongly recommend requesting it from your provider.

What can concep do to help prevent blocklisting? 

As a specialist technology partner, we focus on keeping tight control over our IP reputation, ensuring the highest possible deliverability rates for our clients. Due to the fact we work solely within the Legal, Financial and Professional Services sectors, this provides clients with a lower risk profile due to the nature of communication – purchasing lists and mass mailing is frowned upon in favour of targeted sending to high-value clients and partners. We pride ourselves on our strong client relationships, procedures and policies, outlining good email practice and behaviours we expect from our clients.

Here we have outlined ways in which Concep can assist Professional Services marketers to avoid the threat of blocklisting:


Sign up forms

The Sign-Up Form feature offers a simple method for individual users to capture new contacts. With Sign Up Forms, you can create a series of segmented lists which your contacts can choose to subscribe to. To ensure data hygiene best practices, contacts will only be added to a segmented list after receiving a confirmation email, meaning that you are only adding valid contacts to your database. Naturally, each list would comprise of a different focus area of the business (i.e. Litigation, Real Estate, Tax, etc.) which the contact can opt to subscribe to. This enables you to send targeted comms without an overcomplicated manual process. It also means you can be sure that you're only delivering comms that matter most to your contacts. Subsequently, giving you peace of mind that your deliverability won't be affected by spam reports, in turn reducing the risk of potential blocklisting.

Automated compliance workflows

Gathering consent from existing contacts, as well as capturing it from new contacts is fundamental to any business. Concep provides a solution which utilises automation, to send out emails to gather consent from your contacts. Through implementing an automated workflow, this will enable your firm to send comms to contacts that actually want to receive them, therefore reducing the risk of sending to recycled spam traps and unengaged contacts in your database. Automation doesn’t have to be overly complicated; Concep’s support team are at hand to take you through the streamline process step by step.

Reporting Kits

Reporting and analytics are an essential part of any digital marketer’s strategy. Having access to the data that is beneficial to you and your business can be instrumental in achieving a firms eMarketing goals and objectives. But it takes time and resource to select the metrics that matter and to build a report, we’ve made it easy by creating custom reporting kits focusing on email deliverability and data hygiene. These kits have been designed to help you clear out dirty data, unengaged contacts and help you ensure your communications hit the desired inboxes.

For more information about these kits, click here.

Active list management

For clients, Concep’s email marketing platform has a suppression list feature, allowing marketing teams to actively manage contacts in real-time. This means that any contacts that have hard bounced in a sending account are automatically suppressed from receiving future campaigns. If a hard bounce exists, it simply cannot be added to a new sending list, therefore diminishing the threat of IP blocklisting and the risk of repeat hard bounces being flagged.


Why is an ESPs infrastructure critically important when focusing on the topic of blocklisting? Security, reliability and enhancing performance are key components to the way an ESPs infrastructure is configured. That's why Concep’s Mail Server runs the latest version of PowerMTA (v5.0) which is an industry leader enterprise-grade email message transfer agent (MTA) designed for sending high-volume messages, ensuring optimal deliverability for our clients. Our priority is our client’s peace of mind, so we reduce their blocklisting risk by leveraging an infrastructure which runs active blocklist monitoring and alerting. What’s more, we’ve broken down the benefits:

IP sender reputation

IP sender reputation refers to the reputation of your email sending IP address that email inbox providers use to ascertain whether you are a spammer. Sender reputation is based on factors such as content quality, quality of contacts, and engagement levels with previous emails sent from your IP. It is crucial for your firms email deliverability and risk of blocklisting to be sending comms from an IP with a sender score of 95 or higher.

The Concep team provide best practice deliverability guidelines for clients and actively review sent email campaign statistics to look for campaigns with high bounce rates. These are flagged daily enabling the team to contact clients and advise on the best ways to improve their deliverability. Not only does this assist our clients to improve their practice but ensures that our IP reputation – or sender score - remains consistently very high, reducing the risk of the sending domains or IP’s being added to any blocklists.

Dedicated IP sending

Unlike other ESPs within the Professional Services and Legal space, Concep can offer dedicated IPs for clients. This is ideal for firms who consistently send a high volume of emails on a regular basis, protecting both their sender reputation and that of the rest of our clients. Rest assured, our support team monitors dedicated IP addresses and domains just as closely as the others to ensure you maintain a high sender score. If there are ever any issues, we will assist you in troubleshooting to sustain your performance. Your deliverability is always our highest priority.

Secure Sending

Email encryption allows organisations to protect sensitive messages and increase their compliance with privacy regulations. Concep uses a common encryption method, known as opportunistic TLS, which enables the use of authentication and validation systems such as DKIM and DMARC giving our clients optimum security.

As we have previously mentioned, the setup of DKIM and DMARC is default for all Concep clients. ESPs should not be charging for this as an ‘add-on’ service.